Abstract
AbstractElectromagnetic ultralow‐frequency (ULF) waves are known to play a substantial role in radial transport, acceleration, and loss of relativistic particles trapped in the Earth's outer radiation belt. Using in situ observations by multiple spacecraft operating in the vicinity of outer radiation belts, we analyze the temporal and spatial behavior of ULF waves throughout the geomagnetic storm of 8–9 October 2012 and compare with the dynamics of relativistic electron fluxes on board the twin Van Allen Probes spacecraft. The analysis shows that the relativistic electron fluxes reduce from their prestorm levels during the first phase of the storm and rapidly increase during the second phase of the storm. We demonstrate that the behavior of ULF wave power changes throughout the storm, from ULF oscillations being a mixture of compressional and shear magnetic components during the first phase of the storm to ULF oscillations being dominated by transverse (shear) components during the second phase. We analyze the parameters of ULF‐driven radial diffusion throughout the storm and compare the observed diffusion coefficients with their statistical averages. We demonstrate that the observed diffusion coefficients are strong enough to impact the redistribution of relativistic electron fluxes from and to the outer boundary of radiation belts and the diffusion might influence the effects of any local electron acceleration by transporting fluxes inward or outward according to phase space density gradients.
Highlights
The Earth’s radiation belts are regions of space where energetic particles are trapped by the main magnetic field
In order to address the question whether the ULF waves should be considered as important drivers of radiation belt dynamics along with very low frequency (VLF) chorus and other waves, we examine the behavior of ULF wave power in Pc4 and Pc5 range throughout the 8–9 October 2012 storm, using magnetic field data from two Van Allen Probes, magnetic and electric field data from three Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites [Angelopoulos, 2008] and magnetic field data from three Geostationary Operational Environmental Satellites (GOES) [Singer et al, 1996], and relativistic electron flux data from the Van Allen Probes
Magnetic and electric radial diffusion coefficients associated with ULF waves are derived from THEMIS electric and magnetic observations
Summary
The Earth’s radiation belts are regions of space where energetic particles (from hundreds of keV to tens of MeV) are trapped by the main magnetic field. In this study we are using the approach proposed by Brizard and Chan [2001] and Fei et al [2006] in which the electric (DELL) and magnetic (DBLL) diffusion coefficients are expressed explicitly in terms of the azimuthal electric field PSD and the field-aligned compressional parallel magnetic field PSD, respectively The magnitudes of both diffusion coefficients and the change of relative magnitudes DELL∕DBLL are analyzed throughout the storm as a function of time and as a function of magnetic shells. The observed diffusion coefficients are sufficient enough to potentially impact the redistribution of flux from and to the outer boundary and would impact the effects of any local acceleration by transporting flux down phase space density gradients such as examined by Reeves et al [2013]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
